refactor(dev): remove the unreported MCP protocolEra field

.changeset/remove-protocol-era.md

@@ -0,0 +1,5 @@
+---
+"agent-bundle": minor
+---
+
+Remove `protocolEra` from `DevRuntimeMcpConnectionState` (exported from `agent-bundle/api`) and from the dev server's runtime MCP session snapshots. The MCP client never reported a protocol era, so the field was always absent; runtime MCP App previews no longer refuse a live session for lacking it. (#836)

examples/rsc-agent-runtime/src/dev/rsbuild-runtime-session.ts

@@ -800,7 +800,6 @@ export class RsbuildRuntimeSession implements DevRuntimeSession {
           resources: Object.freeze({}),
           tools: Object.freeze({}),
         }),
-        protocolEra: 'modern',
         protocolVersion: '2025-06-18',
         server: Object.freeze({ name: projectName, version: projectVersion }),
       });

packages/agent-bundle/src/dev/mcp-app-runtime-preview-service.ts

@@ -365,7 +365,7 @@ export class McpAppRuntimePreviewService implements McpAppRuntimeRoutePreviewSer
       throw new Error('Runtime MCP App stable session has foreign provider/state authority.');
     }
     if (
-      live.connection.protocolEra === undefined || live.connection.protocolVersion === undefined ||
+      live.connection.protocolVersion === undefined ||
       live.connection.capabilities === undefined || live.connection.server === undefined
     ) {
       throw new Error('Runtime MCP App stable session has incomplete negotiation.');

packages/agent-bundle/src/dev/mcp-session/mcp-session-types.ts

@@ -52,7 +52,6 @@ export interface McpClient {
   getServerCapabilities(): ServerCapabilities | undefined;
   getServerVersion(): Implementation | undefined;
   getNegotiatedProtocolVersion?(): string | undefined;
-  getProtocolEra?(): 'legacy' | 'modern' | undefined;
   listPrompts(params?: undefined, options?: McpRequestOptions): Promise<{ readonly prompts: readonly Prompt[] }>;
   listResources(params?: undefined, options?: McpRequestOptions): Promise<{ readonly resources: readonly Resource[] }>;
   listResourceTemplates(
@@ -146,7 +145,6 @@ export interface McpSessionResourceOptions extends McpSessionRequestOptions {
 
 export interface McpSessionConnectionState {
   readonly capabilities: ServerCapabilities | undefined;
-  readonly protocolEra: 'legacy' | 'modern' | undefined;
   readonly protocolVersion: string | undefined;
   readonly server: Implementation | undefined;
 }

packages/agent-bundle/src/dev/mcp-session/mcp-session.ts

@@ -640,7 +640,6 @@ export class McpSession {
           this.#capture = connectState.capture;
           this.#connection = Object.freeze({
             capabilities: client.getServerCapabilities(),
-            protocolEra: client.getProtocolEra?.(),
             protocolVersion: client.getNegotiatedProtocolVersion?.(),
             server: client.getServerVersion(),
           });

packages/agent-bundle/src/dev/runtime-mcp-registry.ts

@@ -1154,7 +1154,6 @@ const bindingCopy = (binding: DevRuntimeMcpSessionBinding): DevRuntimeMcpInvalid
 
 const finiteConnectionState = (input: DevRuntimeMcpConnectionState): DevRuntimeMcpConnectionState => Object.freeze({
   capabilities: input.capabilities === undefined ? undefined : jsonObject(input.capabilities, 'Runtime MCP connection capabilities'),
-  protocolEra: input.protocolEra,
   protocolVersion: input.protocolVersion,
   server: input.server === undefined ? undefined : Object.freeze({
     name: nonempty(input.server.name, 'Runtime MCP connection server name'),

packages/agent-bundle/src/dev/runtime-mcp-routes.ts

@@ -132,7 +132,6 @@ const publicSessionSnapshot = (snapshot: DevRuntimeMcpSessionSnapshot): PublicRu
     }),
     connection: Object.freeze({
       capabilities: snapshot.connection.capabilities,
-      protocolEra: snapshot.connection.protocolEra,
       protocolVersion: snapshot.connection.protocolVersion,
       server: server === undefined ? undefined : Object.freeze({ name: server.name, version: server.version }),
     }),

packages/agent-bundle/src/dev/runtime-protocol.ts

@@ -223,7 +223,6 @@ export interface DevRuntimeMcpRegistrySnapshot {
 
 export interface DevRuntimeMcpConnectionState {
   readonly capabilities: JsonObject | undefined;
-  readonly protocolEra: 'legacy' | 'modern' | undefined;
   readonly protocolVersion: string | undefined;
   readonly server: Readonly<{ readonly name: string; readonly version: string }> | undefined;
 }

packages/agent-bundle/tests/dev-server.test.ts

@@ -932,7 +932,7 @@ it('applies the established foreground origin and token guard to MCP session cre
       opens.push(options);
       return {
         binding: { epochId: 'epoch-a', serverName: 'weather', target: 'portable' },
-        connection: { capabilities: {}, protocolEra: 'modern', protocolVersion: '2025-11-25', server: { name: 'fixture', version: '1.0.0' } },
+        connection: { capabilities: {}, protocolVersion: '2025-11-25', server: { name: 'fixture', version: '1.0.0' } },
         id: 'session-a',
       };
     },
@@ -971,7 +971,7 @@ it('applies the established foreground origin and token guard to MCP session cre
     await expect(accepted.json()).resolves.toEqual({
       session: {
         binding: { epochId: 'epoch-a', serverName: 'weather', target: 'portable' },
-        connection: { capabilities: {}, protocolEra: 'modern', protocolVersion: '2025-11-25', server: { name: 'fixture', version: '1.0.0' } },
+        connection: { capabilities: {}, protocolVersion: '2025-11-25', server: { name: 'fixture', version: '1.0.0' } },
         id: 'session-a',
       },
     });
@@ -986,7 +986,7 @@ it('accepts headerless browser same-origin fetch provenance with the exact token
   let streamSubscriptions = 0;
   const session = {
     binding: { epochId: 'epoch-a', serverName: 'weather', target: 'portable' },
-    connection: { capabilities: {}, protocolEra: 'modern', protocolVersion: '2025-11-25', server: { name: 'fixture', version: '1.0.0' } },
+    connection: { capabilities: {}, protocolVersion: '2025-11-25', server: { name: 'fixture', version: '1.0.0' } },
     id: 'session-a',
     subscribeTrace: () => {
       streamSubscriptions += 1;
@@ -1120,7 +1120,7 @@ it('ends active authenticated MCP trace readers before foreground shutdown destr
   let subscriptions = 0;
   const session = {
     binding: { epochId: 'epoch-a', serverName: 'weather', target: 'portable' },
-    connection: { capabilities: {}, protocolEra: 'modern', protocolVersion: '2025-11-25', server: { name: 'fixture', version: '1.0.0' } },
+    connection: { capabilities: {}, protocolVersion: '2025-11-25', server: { name: 'fixture', version: '1.0.0' } },
     id: 'session-a',
     subscribeTrace: () => {
       subscriptions += 1;

packages/agent-bundle/tests/mcp-app-runtime-binding-service.test.ts

@@ -39,7 +39,7 @@ const runVector: RuntimeVector = Object.freeze({
 
 const sessionSnapshot = (): DevRuntimeMcpSessionSnapshot => Object.freeze({
   binding: Object.freeze({ ...runBinding, providerSessionId: 'provider-private', stateStoreId: 'state-private' }),
-  connection: Object.freeze({ capabilities: undefined, protocolEra: 'modern', protocolVersion: '2026-01-26', server: undefined }),
+  connection: Object.freeze({ capabilities: undefined, protocolVersion: '2026-01-26', server: undefined }),
   state: 'ready',
 });
 

packages/agent-bundle/tests/mcp-app-runtime-preview-service.test.ts

@@ -51,7 +51,6 @@ const snapshot = (): DevRuntimeMcpSessionSnapshot => Object.freeze({
   }),
   connection: Object.freeze({
     capabilities: Object.freeze({ resources: Object.freeze({}), tools: Object.freeze({}) }),
-    protocolEra: 'modern' as const,
     protocolVersion: '2026-01-26',
     server: Object.freeze({ name: 'weather', version: '1.0.0' }),
   }),

packages/agent-bundle/tests/mcp-session-routes.test.ts

@@ -29,7 +29,7 @@ const startRoutes = async (service: McpSessionRouteService): Promise<StartedRout
 
 class RecordingSession implements McpSessionRouteSession {
   readonly binding = Object.freeze({ epochId: 'epoch-a', serverName: 'weather', target: 'portable' });
-  readonly connection = Object.freeze({ capabilities: { tools: {} }, protocolEra: 'modern' as const, protocolVersion: '2025-11-25', server: { name: 'fixture', version: '1.0.0' } });
+  readonly connection = Object.freeze({ capabilities: { tools: {} }, protocolVersion: '2025-11-25', server: { name: 'fixture', version: '1.0.0' } });
   readonly id = 'session-a';
   readonly timeoutMs = 5_000;
   readonly calls: unknown[] = [];

packages/agent-bundle/tests/mcp-session-service.test.ts

@@ -1673,7 +1673,6 @@ it('exposes one opaque, epoch-bound session handle with a bounded ordered wire t
           transport.onmessage?.(progressFrame);
         },
         getNegotiatedProtocolVersion: () => '2026-07-28',
-        getProtocolEra: () => 'modern' as const,
         getPrompt: async () => ({ messages: [] }),
         getServerCapabilities: () => ({ logging: {} }),
         getServerVersion: () => ({ name: 'wire-fixture', version: '1.0.0' }),
@@ -1695,7 +1694,6 @@ it('exposes one opaque, epoch-bound session handle with a bounded ordered wire t
     expect(session.binding).toEqual({ epochId: 'epoch-wire', serverName: 'fixture', target: 'portable' });
     expect(Object.isFrozen(session.binding)).toBe(true);
     expect(session.connection).toMatchObject({
-      protocolEra: 'modern',
       protocolVersion: '2026-07-28',
       server: { name: 'wire-fixture', version: '1.0.0' },
     });

packages/agent-bundle/tests/runtime-mcp-registry.test.ts

@@ -39,7 +39,6 @@ const deferred = <T = void>(): Readonly<{
 
 const connectionState: DevRuntimeMcpConnectionState = Object.freeze({
   capabilities: Object.freeze({ tools: Object.freeze({}) }),
-  protocolEra: 'modern',
   protocolVersion: '2025-06-18',
   server: Object.freeze({ name: 'fixture', version: '1.0.0' }),
 });

packages/agent-bundle/tests/runtime-mcp-routes.test.ts

@@ -25,7 +25,6 @@ it('delegates the fixed manual runtime MCP open route without becoming an App pr
     }),
     connection: Object.freeze({
       capabilities: Object.freeze({}),
-      protocolEra: 'modern' as const,
       protocolVersion: '2026-01-26',
       server: Object.freeze({ name: 'weather', providerSessionId: 'provider-private', stateStoreId: 'state-private', unexpected: 'unexpected-value', version: '1.0.0' }),
     }),
@@ -38,7 +37,6 @@ it('delegates the fixed manual runtime MCP open route without becoming an App pr
     }),
     connection: Object.freeze({
       capabilities: Object.freeze({ tools: Object.freeze({ listChanged: true }) }),
-      protocolEra: 'modern' as const,
       protocolVersion: '2026-02-09',
       server: Object.freeze({ name: 'weather-next', providerSessionId: 'provider-private', stateStoreId: 'state-private', unexpected: 'unexpected-value', version: '2.0.0' }),
     }),
@@ -92,7 +90,7 @@ it('delegates the fixed manual runtime MCP open route without becoming an App pr
     expect(opened).toEqual({ session: { binding: {
       definitionDigest: 'definition-a', registryRevision: 3, serverDigest: 'server-a', serverName: 'weather',
       sessionId: 'session-a', sessionRevision: 2, target: 'portable', transportDigest: 'transport-a',
-    }, connection: { capabilities: {}, protocolEra: 'modern', protocolVersion: '2026-01-26', server: { name: 'weather', version: '1.0.0' } }, state: 'ready' } });
+    }, connection: { capabilities: {}, protocolVersion: '2026-01-26', server: { name: 'weather', version: '1.0.0' } }, state: 'ready' } });
     expect(JSON.stringify(opened)).not.toContain('provider-private');
     expect(JSON.stringify(opened)).not.toContain('state-private');
 
@@ -113,7 +111,7 @@ it('delegates the fixed manual runtime MCP open route without becoming an App pr
           definitionDigest: 'definition-b', registryRevision: 4, serverDigest: 'server-b', serverName: 'weather',
           sessionId: 'session-a', sessionRevision: 3, target: 'portable', transportDigest: 'transport-b',
         },
-        connection: { capabilities: { tools: { listChanged: true } }, protocolEra: 'modern', protocolVersion: '2026-02-09', server: { name: 'weather-next', version: '2.0.0' } },
+        connection: { capabilities: { tools: { listChanged: true } }, protocolVersion: '2026-02-09', server: { name: 'weather-next', version: '2.0.0' } },
         state: 'ready',
       },
     });
@@ -136,7 +134,7 @@ it('claims manual runtime MCP routes before the generic runtime browser API', as
           snapshot: () => Object.freeze({ binding: Object.freeze({
             definitionDigest: 'definition-a', providerSessionId: 'provider-private', registryRevision: 3, serverDigest: 'server-a', serverName: 'weather',
             sessionId: 'session-a', sessionRevision: 2, stateStoreId: 'state-private', target: 'portable', transportDigest: 'transport-a',
-          }), connection: Object.freeze({ capabilities: Object.freeze({}), protocolEra: 'modern' as const, protocolVersion: '2026-01-26', server: undefined }), state: 'ready' as const }),
+          }), connection: Object.freeze({ capabilities: Object.freeze({}), protocolVersion: '2026-01-26', server: undefined }), state: 'ready' as const }),
           watchClosed: () => Object.freeze({ closed: false, unsubscribe: () => undefined }),
         });
       },

packages/workbench/src/mcp/mcp-app-client.ts

@@ -312,11 +312,6 @@ const runtimeStringOrUndefined = (value: unknown, label: string): string | undef
   return runtimeInvalid(`Runtime MCP App route returned an invalid ${label}.`);
 };
 
-const runtimeEra = (value: unknown): 'legacy' | 'modern' | undefined => {
-  if (value === undefined || value === 'legacy' || value === 'modern') return value;
-  return runtimeInvalid('Runtime MCP App route returned an invalid protocol era.');
-};
-
 const runtimeProfileId = (value: unknown): 'portable' | 'chatgpt' | 'claude' => {
   if (value === 'portable' || value === 'chatgpt' || value === 'claude') return value;
   return runtimeInvalid('Runtime MCP App route returned an invalid profile.');
@@ -389,19 +384,16 @@ const runtimeBinding = (value: unknown): McpAppRuntimeBindingSnapshot => {
 
 const runtimeConnection = (value: unknown): Readonly<{
   readonly capabilities: Readonly<Record<string, McpAppJsonValue>> | undefined;
-  readonly protocolEra: 'legacy' | 'modern' | undefined;
   readonly protocolVersion: string | undefined;
   readonly server: Readonly<{ readonly name: string; readonly version: string }> | undefined;
 }> => {
-  const record = runtimeRecord(value, ['capabilities', 'protocolEra', 'protocolVersion', 'server']);
+  const record = runtimeRecord(value, ['capabilities', 'protocolVersion', 'server']);
   if (record.capabilities !== undefined && !isRecord(record.capabilities)) runtimeInvalid('Runtime MCP App route returned invalid server capabilities.');
   const server = record.server === undefined ? undefined : runtimeRecord(record.server, ['name', 'version']);
   const capabilities = record.capabilities === undefined ? undefined : asRecord(record.capabilities);
-  const protocolEra = runtimeEra(record.protocolEra);
   const protocolVersion = runtimeStringOrUndefined(record.protocolVersion, 'protocol version');
   return Object.freeze({
     capabilities,
-    protocolEra,
     protocolVersion,
     server: server === undefined ? undefined : Object.freeze({ name: runtimeText(server.name, 'server name'), version: runtimeText(server.version, 'server version') }),
   });

packages/workbench/src/mcp/mcp-route-client.ts

@@ -22,7 +22,6 @@ export interface McpRouteSessionBinding {
 
 export interface McpRouteConnection {
   readonly capabilities?: unknown;
-  readonly protocolEra?: 'legacy' | 'modern';
   readonly protocolVersion?: string;
   readonly server?: Readonly<{ readonly name: string; readonly version: string }>;
 }
@@ -220,15 +219,13 @@ const routeConnection = (value: unknown): McpRouteConnection => {
     serverSnapshot = Object.freeze({ name: server.name, version: server.version });
   }
   if (
-    !hasOnlyKeys(connection, ['capabilities', 'protocolEra', 'protocolVersion', 'server']) ||
-    (connection.protocolEra !== undefined && connection.protocolEra !== 'legacy' && connection.protocolEra !== 'modern') ||
+    !hasOnlyKeys(connection, ['capabilities', 'protocolVersion', 'server']) ||
     (connection.protocolVersion !== undefined && typeof connection.protocolVersion !== 'string')
   ) {
     throw new McpRouteClientError('AB8019', 'Foreground MCP route returned an invalid connection.');
   }
   return Object.freeze({
     ...(connection.capabilities === undefined ? {} : { capabilities: connection.capabilities }),
-    ...(connection.protocolEra === undefined ? {} : { protocolEra: connection.protocolEra }),
     ...(connection.protocolVersion === undefined ? {} : { protocolVersion: connection.protocolVersion }),
     ...(serverSnapshot === undefined ? {} : { server: serverSnapshot }),
   });

packages/workbench/src/mcp/mcp-session-controller.ts

@@ -294,7 +294,6 @@ const isRuntimeBinding = (value: unknown): value is DevRuntimeMcpAppRunBinding =
 
 const isRuntimeConnection = (value: unknown): value is McpRouteConnection => {
   if (!isRecord(value)) return false;
-  if (value.protocolEra !== undefined && value.protocolEra !== 'legacy' && value.protocolEra !== 'modern') return false;
   if (value.protocolVersion !== undefined && typeof value.protocolVersion !== 'string') return false;
   if (value.server !== undefined && (!isRecord(value.server) || typeof value.server.name !== 'string' || typeof value.server.version !== 'string')) return false;
   return true;

packages/workbench/tests/agent-bundle-remote-transport.test.ts

@@ -63,7 +63,6 @@ const cancellableStream = (): Readonly<{ readonly cancelled: () => boolean; read
 const binding = Object.freeze({ epochId: 'epoch-a', serverName: 'weather', target: 'portable' });
 const connection = Object.freeze({
   capabilities: { tools: {} },
-  protocolEra: 'modern',
   protocolVersion: '2025-11-25',
   server: { name: 'weather-fixture', version: '1.0.0' },
 });
@@ -685,7 +684,7 @@ it('uses only exact runtime MCP routes and preserves the operation vector', asyn
     },
     connection: {
       capabilities: { resources: { listChanged: true }, tools: { listChanged: true } },
-      protocolEra: 'modern', protocolVersion: '2026-02-09', server: { name: 'weather-next', version: '2.0.0' },
+      protocolVersion: '2026-02-09', server: { name: 'weather-next', version: '2.0.0' },
     },
     state: 'ready',
   };

packages/workbench/tests/mcp-app-client.test.ts

@@ -146,7 +146,7 @@ const runtimePreview = Object.freeze({
       definitionDigest: 'definition-a', registryRevision: 3, serverDigest: 'server-a', serverName: 'weather',
       sessionId: 'runtime-session-a', sessionRevision: 2, target: 'portable', transportDigest: 'transport-a',
     }),
-    connection: Object.freeze({ capabilities: Object.freeze({ tools: Object.freeze({}) }), protocolEra: 'modern', protocolVersion: '2026-01-26', server: Object.freeze({ name: 'weather', version: '1.0.0' }) }),
+    connection: Object.freeze({ capabilities: Object.freeze({ tools: Object.freeze({}) }), protocolVersion: '2026-01-26', server: Object.freeze({ name: 'weather', version: '1.0.0' }) }),
     state: 'ready',
   }),
 });